<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<style>
			.ani{
				width: 100px;
				height: 100px;
				background-color: #FF0000;
				transition: width 2s;
			}
			.ani:hover{
				 width: 300px;
				 
			}
		</style>
	</head>
	<body>
		<h1>拉伸一个盒子</h1>
		<div class="ani"></div>
	</body>
</html>
